<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>计算圆的面积</title>
    <script>
        var radii = prompt("请输入圆的半径");
        var x = Math.PI
        alert(parseInt(radii)*parseInt(radii)*x);
    </script>
</head>
<body>
    
</body>
</html>